The SKIBI study: Comparative early outcomes of five minimally invasive glaucoma surgeries combined with cataract extraction in Indian patients with primary open-angle glaucoma

Abstract

Purpose:

To evaluate and compare the early clinical outcomes of five microinvasive glaucoma surgery (MIGS) techniques—Suture-Gonioscopy-Assisted Transluminal Trabeculotomy (Suture-GATT), Kahook Dual Blade (KDB), iStent, Bent Ab Interno Needle Goniectomy (BANG), and iStent inject—combined with phacoemulsification, in a real-world cohort of Indian patients with primary open-angle glaucoma (POAG) and coexisting cataract.

Methods:

This prospective observational study included 113 eyes of 113 patients undergoing MIGS with phacoemulsification at a tertiary care center. Patients were allocated to one of five MIGS groups in a nonrandomized fashion through shared decision-making based on clinical profile, affordability considerations, and device availability. The procedures included Suture-GATT (21 eyes), KDB (28 eyes), iStent (20 eyes), BANG (31 eyes), and iStent inject (13 eyes). The intraocular pressure (IOP) and antiglaucoma medication (AGM) use were recorded at baseline and at 1 week, 1 month, 3 months, and 6 months postoperatively. Safety and complications were also assessed.

Results:

All procedures led to significant IOP and AGM reduction at 6 months (P < 0.05). Numerically greater mean IOP reduction was observed in the Suture-GATT group (6.41 ± 2.05 mmHg), with 71% achieving complete success. iStent inject and KDB also showed favorable outcomes. IStent-based procedures had the lowest complication rates.

Conclusion:

In real-world clinical practice, MIGS combined with cataract surgery offers a safe and effective option for IOP and medication reduction across a range of POAG severities. Procedure selection is influenced by patient-specific factors, including cost and device availability, underscoring the importance of individualized care in resource-variable settings.

Glaucoma, a chronic and progressive optic neuropathy, remains a leading cause of irreversible blindness globally. Affecting millions, it is primarily characterized by damage to the optic nerve, often associated with elevated intraocular pressure (IOP). Left untreated, glaucoma progresses insidiously, beginning with peripheral vision loss and culminating in central blindness. By 2040, the number of individuals affected is projected to rise to 111.8 million worldwide, highlighting the urgency for effective treatment strategies. Current interventions aim to reduce IOP to halt disease progression, with options ranging from pharmacological and laser therapies to surgical procedures tailored to the severity and subtype of glaucoma.[1,2]

Traditional glaucoma surgeries like trabeculectomy and drainage devices, though effective, require long recovery times, frequent follow-ups, and carry risks. This creates a treatment gap, compounded by barriers like poor medication adherence and drop intolerance.

Minimally invasive glaucoma surgery (MIGS) has emerged as a transformative approach, bridging the gap between conventional therapies and more invasive surgeries. Coined by Dr. Ike Ahmed in 2009, MIGS techniques are defined by their smaller incisions, faster recovery, and improved safety profile compared to traditional surgeries.[3]

MIGS encompasses a range of techniques that enhance aqueous outflow via trabecular meshwork incision or bypass, including procedures such as Suture-Gonioscopy-Assisted Transluminal Trabeculotomy (Suture-GATT), Kahook Dual Blade (KDB) goniotomy, Bent Ab Interno Needle Goniectomy (BANG), and micro-stent implantation like iStent and iStent inject. These procedures are increasingly used to reduce medication burden or as early surgical interventions before exhausting all medical and laser options.[4,5,6]

Previous clinical studies have reported that trabeculotomy-based MIGSs such as GATT result in IOP reductions of 5–12 mmHg with 60–90% surgical success at 6–12 months, while KDB excisional goniotomy typically lowers IOP by 4–10 mmHg and reduces medication burden by 25–40%.[7,8,9,10,11,12,13] Similarly, stent-based procedures including iStent and iStent inject demonstrate a 3–8 mmHg reduction in IOP with a favorable safety profile and fewer postoperative complications.[9,10,13] Most of these data are derived from Western cohorts.

In the real-world Indian clinical environment, procedure selection is strongly influenced not only by disease characteristics but also by socioeconomic factors, affordability, device accessibility, and surgeon–patient shared decision-making, particularly when combined with cataract surgery – a frequent requirement in this population. Recent Indian reports support the feasibility and safety of MIGS in clinical practice, yet published data largely focus on single procedures evaluated in isolation.[14,15] Comparative real-world evidence across multiple MIGS techniques remains limited, especially in the context of resource variability and individualized decision-making. Therefore, we conducted a prospective, nonrandomized study to compare early IOP reduction, change in medication burden, and safety profiles of five commonly used MIGS procedures performed with phacoemulsification in Indian patients with POAG. This study aims to fill a critical knowledge gap and provide practical insights to support individualized MIGS selection in the Indian clinical context.

Methods

This prospective, nonrandomized comparative study was conducted at a tertiary eye care center in South India between May and October 2023. Ethical approval was obtained from the Institutional Ethics Committee, and all procedures adhered to the tenets of the Declaration of Helsinki. A cohort of 113 patients diagnosed with mild to moderate POAG, currently managed with antiglaucoma medications (AGMs) and concomitant visually significant cataract, were consecutively enrolled after providing informed consent.

Patients were selected for combined cataract and MIGS surgery based on clinical indication and patient preference after detailed counseling; no randomization or stratified allocation was performed. Participants underwent one of five MIGS procedures—Suture-GATT, KDB (New World Medical, Rancho Cucamonga, CA, USA), BANG, iStent (Glaukos Corporation, San Clemente, CA, USA), or iStent inject (Glaukos Corporation, San Clemente, CA, USA)—in conjunction with phacoemulsification. Procedure selection considered disease severity, affordability, device availability, and patient preference. All surgeries were performed by a single experienced glaucoma surgeon to minimize intersurgeon variability. All procedures were performed ab interno under gonioscopic visualization through a temporal clear corneal incision. Suture-GATT involved a 360° circumferential trabeculotomy to achieve complete Schlemm’s canal cleavage. For KDB and BANG procedures, a wide nasal arc of approximately 120°–180° of trabecular meshwork was excised or goniectomized, respectively, with minor variability based on angle visibility and patient eye movement. iStent implantation consisted of placing one trabecular micro-bypass device into the nasal angle to optimize collector channel access, whereas iStent inject involved placement of two microstents separated by approximately 2–3 clock hours to enhance aqueous outflow distribution. The extent of angle treatment and implant positioning were tailored to maximize visualization and safety in each case.

Primary endpoints included intraocular pressure (IOP) reduction from baseline, a decrease in AGM burden, and the proportion of patients achieving a reduction of more than one AGM. Secondary outcomes encompassed rates of complete success (defined as IOP between 5 and 21 mmHg without AGMs), qualified success (same IOP range with AGMs), and failure (failure to meet IOP criteria or need for reoperation). Postoperative complications were rigorously documented and included sight-threatening events such as hypotony, choroidal detachment, cyclodialysis, persistent hyphema, and loss of light perception. Patients were systematically evaluated at 1 week, 1 month, 3 months, and 6 months postoperatively, with IOP and AGM usage recorded at each visit. Gonioscopic assessment was performed at follow-up visits, and Anterion (Heidelberg Engineering GmbH, Heidelberg, Germany) anterior segment optical coherence tomography (OCT) imaging was performed at 6 months to assess angle anatomy and surgical site status.

Data were managed using Microsoft Excel and analyzed with SPSS version 20 (IBM Corp., USA). Continuous variables were summarized as means ± standard deviations. Paired t-tests were utilized for intragroup comparisons, with statistical significance set at P < 0.05. Intergroup comparisons were performed using ANOVA where appropriate.

Results

The study included 113 eyes of 113 patients who underwent one of five MIGS procedures combined with cataract surgery. The mean age varied significantly among groups (P = 0.042), ranging from 59.25 ± 7.53 years in the Suture-GATT group to 66.33 ± 5.70 years in the iStent inject group. Gender distribution was similar across all groups (P = 0.918). Baseline IOP ranged from 20.28 ± 6.13 mmHg in the BANG group to 23.25 ± 7.17 mmHg in the Suture-GATT group (P = 0.590), and baseline AGM usage ranged from 1.07 ± 0.86 in BANG to 2.07 ± 1.79 in iStent inject patients (P < 0.001). Disease severity was significantly different between groups (P = 0.008), with mild glaucoma more common in the iStent and iStent inject cohorts, and moderate to severe disease prevalent in the Suture-GATT and BANG groups [Table 1].

Table 1.

Demographic and baseline ocular characteristics according to all-procedure groups

Patient characteristics	Suture GATT n=21	KDB n=28	iStent n=20	BANG n=31	iStent inject n=13	P
Age (years)	59.25±7.53	62.87±6.97	65.19±6.12	60.53±8.29	66.33±5.70	0.042*
Baseline IOP (mmHg)	23.25±7.17	22.83±6.13	21.50±6.90	20.28±6.13	22.07±6.49	0.590*
Baseline AGM	1.63±0.69	1.16±0.97	1.82±0.98	1.07±0.86	2.07±1.79	<0.001*
Gender
Male	13 (61.91%)	16 (57.14%)	10 (50%)	18 (58.06%)	7 (53.85%)	0.918#
Female	8 (38.09%)	12 (42.86%)	10 (50%)	13 (41.94%)	6 (46.15%)
Glaucoma Stage
Mild	3 (14.29%)	6 (21.43%)	14 (70%)	2 (6.45%)	10 (76.92%)	0.008#
Moderate	10 (47.62%)	15 (53.57%)	5 (25%)	17 (54.84%)	3 (23.08%)
Severe	8 (38.09%)	7 (25%)	1 (5%)	12 (38.71%)	0
Laterality
RE	11 (52.38%)	15 (53.57%)	9 (45%)	17 (54.84%)	7 (53.85%)	0.972#
LE	10 (47.62%)	13 (46.43%)	11 (55%)	14 (45.16%)	6 (46.15%)

*ANOVA (intergroup comparisons); ^#Chi-Square test

All five MIGS procedures resulted in significant within-group reductions in IOP and AGM usage over 6 months (P < 0.05). The Suture-GATT group demonstrated a numerically greater mean IOP reduction (6.41 ± 2.05 mmHg), followed by iStent inject (6.14 ± 1.98 mmHg), KDB (5.88 ± 1.89 mmHg), BANG (5.27 ± 2.22 mmHg), and iStent (2.81 ± 1.45 mmHg) [Table 2].

Table 2.

Intraocular pressure (IOP) from baseline to 6 months post-surgery for all procedures

Time Point	Suture GATT n=21*	KDB n=28*	iStent n=20*	BANG n=31*	iStent inject n=13*	PΔ (intergroup comparison)
Baseline	23.25±7.17	22.83±6.13	21.50±6.90	20.28±6.13	22.07±6.49	0.590
One Week	15.05±3.67 (P=0.001)	22.16±4.77 (P=0.671)	16.82±4.14 (P=0.044)	14.07±3.92 (P=0.001)	18.20±4.01 (P=0.067)	0.001
One Month	18.83±4.90 (P=0.004)	16.81±5.36 (P=0.013)	18.18±5.24 (P=0.058)	16.18±5.17 (P=0.048)	21.53±4.23 (P=0.589)	0.152
Three Month	17.17±3.20 (P=0.001)	17.04±4.81 (P=0.023)	18.73±5.74 (P=0.065)	15.71±3.69 (P=0.023)	16.53±5.12 (P=0.014)	0.021
Six Month	16.84±5.12 (P=0.001)	16.95±5.49 (P=0.005)	18.69±5.97 (P=0.070)	15.01±5.45 (P=0.014)	15.93±4.27 (P=0.001)	<0.001

*Paired Sample t-test (intragroup comparisons); i.e., P value in each cell for IOP at that time point vs. baseline. ^ΔANOVA (intergroup comparisons)

AGM burden also declined notably across all groups. Suture-GATT patients reduced from a mean of 1.63 to 0.58 AGMs, KDB from 1.16 to 0.62, and BANG from 1.07 to 0.49. The iStent group showed a relatively larger absolute AGM reduction (1.82 to 0.36), corresponding to its higher baseline usage [Table 3]. Complete surgical success (IOP 5–21 mmHg without AGMs and ≥20% IOP reduction) was more frequently observed in the Suture-GATT group (71%), followed by KDB (68%), iStent (60%), iStent inject (54%), and BANG (48%). Failure rates ranged from 10% in Suture-GATT to 26% in BANG [Fig. 1]. Postoperative complications were generally mild and self-limiting but varied among groups. The BANG group showed the highest complication rate, including hyphema (n = 1), peripheral anterior synechiae (PAS) (n = 2), and choroidal folds without hypotony (n = 2). In the Suture-GATT group, three cases of hyphema and one intraoperative false passage were noted. The KDB group had three cases of microhyphema, while the iStent and iStent inject groups each reported a single case of PAS. All surgical groups showed a decrease in AGM burden, with the iStent group demonstrating the greatest mean reduction (1.46 ± 0.38), followed by the Suture-GATT group (1.05 ± 0.26).

Table 3.

Anti-Glaucoma Medication (AGM) from baseline to 6 months post-surgery for all procedures

Time Point	Suture GATT	KDB	iStent	BANG	iStent inject	PΔ (intergroup comparison)
Baseline	1.63±0.69	1.16±0.97	1.82±0.98	1.07±0.86	2.07±1.79	<0.001
One Week	0.39±0.33 (P=0.038)	1.02±0.80 (P=0.872)	0.73±0.65 (P=0.067)	0.79±0.72 (P=0.421)	0.33±0.72 (P=0.001)	<0.001
One Month	0.87±0.45 (P=0.044)	0.76±0.71 (P=0.065)	0.73±0.56 (P=0.073)	0.57±0.80 (P=0.029)	0.73±1.03 (P=0.003)	<0.001
Three Month	0.62±0.38 (P=0.025)	0.66±0.68 (P=0.043)	0.27±0.59 (P=0.032)	0.52±0.75 (P=0.025)	1.40±1.69 (P=0.038)	<0.001
Six Month	0.58±0.43 (P=0.012)	0.62±0.82 (P=0.019)	0.36±0.67 (P=0.038)	0.49±0.78 (P=0.012)	1.43±1.47 (P=0.015)	<0.001

*Paired Sample t-test (intragroup comparisons); i.e., P value in each cell for IOP at that time point vs. baseline. ^ΔANOVA (intergroup comparisons)

Figure 1.

Comparative success rates showing the distribution of complete success, qualified success, and failure across the five MIGS procedures at 6 months

Intergroup comparisons at 6 months revealed statistically significant differences in both IOP reduction and medication burden (P < 0.001).

Discussion

This study evaluated the early clinical outcomes of five MIGS – Suture GATT, KDB, BANG, iStent, and iStent inject – performed in combination with cataract surgery among Indian patients diagnosed with mild to moderate POAG. Surgical choice was based on shared decision-making, incorporating patient preference and surgeon discretion. This nonrandomized approach introduces a potential selection bias, and factors such as socioeconomic status, insurance coverage, and affordability were not systematically recorded. These elements warrant dedicated investigation in future studies to understand their impact on procedure choice and outcomes.

Anterior segment imaging using Anterion offered valuable postoperative anatomical insights across the different MIGS techniques.[16] KDB created a characteristic W-shaped cleft in the trabecular meshwork. BANG resulted in an irregular, rugged incision. Suture-GATT produced a continuous 360-degree cleft, often likened to a bird-beak configuration, and the iStents appeared as a hyper-reflective implant with posterior back-shadowing in the anterior chamber angle. These imaging features not only confirmed the surgical outcomes but also illustrated the anatomical variations created by each MIGS approach. Although AS-OCT provided valuable descriptive information on the postsurgical angle anatomy across MIGS procedures, the lack of standardized preoperative imaging limits our ability to quantify or directly attribute these changes to surgery. This introduces potential interpretation bias, and future studies should incorporate pre- and postoperative imaging at defined intervals for more robust analysis.

In terms of clinical outcomes, all five MIGS procedures achieved a statistically significant reduction in IOP and AGM usage over the 6-month follow-up period. These findings support the expanding role of MIGS combined with phacoemulsification as an effective approach for reducing IOP and medication burden. Among the groups, Suture-GATT showed a numerically greater mean IOP reduction (6.41 mmHg), likely due to the 360-degree trabeculotomy allowing extensive aqueous outflow.[7,8] This was closely followed by iStent inject (6.14 mmHg) and KDB (5.88 mmHg). BANG demonstrated a moderate decline (5.27 mmHg), while the iStent group showed the least IOP reduction (2.81 mmHg). However, these trends should be interpreted cautiously due to baseline severity differences, unequal sample sizes, and the nonrandomized design.

With regard to AGM burden, all surgical groups experienced a decline in medication usage. Notably, iStent patients had the highest mean reduction (1.46 ± 0.38), followed by Suture-GATT (1.05 ± 0.26); however, it is important to note that the iStent cohort primarily consisted of patients with mild POAG, whereas the Suture-GATT cohort comprised those with moderate–severe POAG. These findings suggest that, beyond IOP control, MIGSs also reduce the dependency on topical therapy, which may improve long-term adherence and quality of life.

The present findings align with previous studies. Hamze et al.[9] reported that phaco-GATT achieved a greater IOP reduction and required fewer medications than phaco-iStent, although iStent had a better safety profile, making it suitable for high-risk patients. A 2022 systematic review confirmed that combining iStent with phacoemulsification achieved significantly better IOP and medication outcomes compared to phacoemulsification alone.[10] Ayub et al. (2024)[11] compared BANG and GATT in a randomized trial, and Bukke et al. (2024)[12] found that BANG combined with phacoemulsification achieved a 31.8% reduction in IOP and a 24.3% reduction in AGM use, with 87.5% surgical success at 12 months. Similarly, Salimi et al. (2024) reported that KDB combined with cataract surgery led to a 26% reduction in IOP and a 29% decrease in medication burden, with a favorable safety profile and 25% of patients becoming medication-free.[13]

Complications in our cohort were minimal and varied among groups. The BANG group experienced the highest number of complications (n = 5), including two cases of choroidal folds without hypotony or visual impairment, one case of prolonged hyphema, and two cases of peripheral anterior synechiae (PAS) detected at 6 months. In the Suture-GATT group, there were four complications: three cases of transient hyphema and one intraoperative false passage. The KDB group had three instances of microhyphema. Both iStent and iStent inject had the lowest complication rates, each reporting only one case of synechiae. These findings underscore the importance of surgical technique, case selection, and appropriate patient counseling. The higher frequency of complications in the BANG cohort may be attributed to the relatively greater variability in tissue traction and trabecular meshwork engagement inherent to needle-based goniectomy techniques. Although both KDB and BANG involve trabecular excision, the dedicated dual-blade design of KDB typically allows more controlled, uniform tissue removal, whereas BANG may produce a more irregular cleft, which could predispose to hyphema or localized PAS formation.

Although numerical differences were observed between groups, these comparative findings should be interpreted cautiously as exploratory due to baseline imbalance, varying disease severity, and small subgroup sizes, particularly iStent inject. Severity distribution was not uniform across groups, with a higher proportion of severe cases in Suture-GATT and BANG cohorts, which may have influenced comparative outcomes. Larger, randomized controlled trials are necessary to draw more definitive conclusions regarding comparative efficacy and safety.

In terms of treatment success, Suture-GATT demonstrated a higher proportion achieving a complete success rate of 71% and an overall success rate of 90%. This was followed by KDB, iStent inject, iStent, and BANG. It is important to note that although the iStent group achieved relatively modest IOP reduction, the complete success rate was comparatively high. This likely reflects the lower baseline IOP, higher baseline medication burden, and predominance of mild glaucoma cases in this cohort, where reducing or eliminating topical therapy contributed significantly to meeting success criteria. These factors highlight the influence of baseline differences and treatment goals in defining “success” and reinforce that apparent between-group differences must be interpreted with caution. The highest failure rate was observed in the BANG group (26%), followed by iStent (20%), iStent inject (15%), and KDB (14%), with the lowest failure rate in the Suture-GATT group (10%). The numerically greater performance of Suture-GATT may be related to its more invasive and comprehensive mechanism of action, which might provide more robust IOP control in patients with moderate disease. In contrast, less invasive procedures like BANG and iStent may be less effective in such patients, thereby accounting for their higher failure rates.

While this study provides meaningful early insights into the comparative outcomes of various MIGS procedures in an Indian cohort, several limitations must be acknowledged. It was a single-center, single-surgeon, open-label study, which may limit external generalizability. The surgical procedure was selected based on shared decision-making, rather than a standardized allocation protocol, potentially introducing selection bias. Because allocation was nonrandomized and driven by socioeconomic and clinical considerations, significant baseline imbalances were present, with more severe glaucoma and higher baseline IOP disproportionately represented in the Suture-GATT and BANG cohorts. This introduces substantial selection bias and limits the strength of intergroup comparisons. Additionally, socioeconomic determinants such as affordability and insurance status, which are known to influence procedure selection, were not formally analyzed. In the Indian setting, affordability and device availability are major determinants of MIGS utilization in real-world practice. Implant-based options such as iStent and iStent inject require proprietary devices, which may not be accessible in all centers and increase overall surgical cost, resulting in lower uptake despite favorable safety. By contrast, trabecular bypass and excisional goniotomy techniques using reusable or lower-cost instruments (including Suture-GATT, KDB, and BANG) are more widely available and financially feasible for many patients who often bear out-of-pocket treatment expenses. These access-related factors likely contributed to the distribution of procedures observed in this study.[14,15] Thus, the influence of economic constraints on procedure allocation and outcomes remains incompletely assessed. Some subgroups—particularly the iStent inject cohort (n = 13)—were relatively small and may be underpowered for detecting statistically significant intergroup differences. Therefore, these comparative findings should be interpreted as exploratory rather than definitive. The 6-month follow-up period, though appropriate for assessing early outcomes, does not reflect long-term efficacy or safety. A larger cohort with longer observation is needed to evaluate durability of IOP control, medication independence, and maintenance of outflow patency following each MIGS technique. A stratified subgroup analysis based on disease severity would provide more robust comparative insight and is planned in future extended follow-up. Furthermore, including patients with secondary glaucoma and extending the follow-up period would provide a more comprehensive understanding of the treatments’ efficacy and safety in a broader patient population.[17,18,19] Despite these constraints, the study contributes valuable real-world data and emphasizes the utility of anterior segment imaging in assessing post-MIGS anatomical outcomes. Larger, randomized, multicenter studies with extended follow-up are warranted to validate and expand upon these early findings. As the present study reports outcomes only up to 6 months, extended observation is essential to assess the durability of IOP reduction, sustained medication independence, and long-term stability of angle anatomy following each technique. Longer-term data will also better characterize safety, including the persistence of outflow patency and the risk of late failure or need for reintervention.

Conclusion

In conclusion, all five MIGS procedures combined with phacoemulsification demonstrated clinically meaningful reductions in intraocular pressure and antiglaucoma medication burden in patients with primary open-angle glaucoma. Among these, Suture-GATT and iStent inject achieved the greatest IOP reduction. The iStent inject group exhibited a favorable safety profile with minimal complications; however, its higher postoperative medication requirement and limited cost-effectiveness may constrain its widespread applicability, particularly in resource-limited settings.

Suture-GATT, in contrast, demonstrated encouraging IOP and medication reductions with an acceptable safety profile and the lowest failure rate, making it a particularly promising option in this population. KDB excisional goniotomy also demonstrated favorable outcomes, with consistent IOP control and reduced medication dependence. Compared to BANG, the KDB group exhibited a notably lower failure rate and a higher proportion of eyes achieving target IOP with reduced medication use at 6 months, suggesting greater procedural sustainability.

Overall, while Suture-GATT and iStent inject demonstrated numerically greater reduction, KDB emerges as a viable and reliable alternative. These findings underscore the importance of individualized MIGS selection based on clinical efficacy, safety, and economic considerations. Further multicenter, randomized controlled trials with longer follow-up are warranted to validate these results and guide evidence-based surgical decision-making in the management of POAG with coexisting cataract.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.